1. Field of the Invention
The present invention relates to a method and apparatus for testing individual remote transponders, particularly RFID transponders. The invention also relates to a corresponding testing system.
2. Description of Background Art
Manufacturers of RFID transponders typically test every transponder they make either on the manufacturing line, or in immediately subsequent process stages. If transponder manufacture is automated, the aim is to perform testing on the manufacturing line. The most common form of testing is to try to read the contents of the transponder in a reactive field, using an RFID reader and a near-field antenna. If reading fails, the transponder is flagged as faulty.
In the case of UHF transponders, a problem in this form of testing is that transponders with a performance significantly below the target level pass the test. This is because even faulty transponders can be successfully read a reactive field (near field), but in a radiating field (far field) their reading distance is so small that in practice they are useless. In addition, if it is wished to make performance measurements during testing, for example by measuring how much power is required to activate the transponder, or how strong a response is received from it, it is difficult or even impossible to apply measurement results obtained in a reactive field to real usetaking place in a radiating field.
One solution to this is to test transponders directly in a radiating field. Such testing is indeed presently done and, on the market, it brings added value particularly to more expensive transponders with a higher processing value. However, there is a problem during testing that on the manufacturing line and often also in the various processing stages of the delivery chain the transponders are very close to each other and it is difficult to measure an individual transponder in a radiation field in the presence of other transponders. Various solutions for this have been presented, such as selecting the transponder to be measured on the basis of its memory content and screening the surrounding transponders or inactivating them for the duration of the detection. However these solutions have their own practical problems. A screening structure should be designed separately for each type of transponder, with the consequent additional engineering work. For their part, the memory contents of the transponders on the manufacturing line are often the same, so that sorting cannot be performed on their basis.
There are many publications relating to quality control of RIFD transponders, active players in the sector being at least Avery Dennison as a transponder manufacturer and Mühlbauer as a device manufacturer. Patent (application) publications dealing with the present subject in general as well as proposing specific testing solutions are at least EP 1990784, EP 1989559, and CN 10103361, US 2006/0012387, US 2006/271328, and US 2006/226983.